In recent years, a core molding method using a rigid core has been proposed in order to mold a pneumatic tire accurately, as shown in the Patent documents 1 and 2. The rigid core includes an outer surface having substantially same shape with an inner surface of the tire. The rigid core can be divided into a plurality of core segments which are movable radially inward of the tire. In the core molding method, unvulcanized rubber components, e.g. an inner liner, a carcass ply, a belt ply, a sidewall rubber, and a tread rubber are sequentially arranged on the outer surface of the rigid core to form a green tire thereon. The green tire with the rigid core is inserted in a space of a vulcanization mold, and then the green tire is vulcanized between the rigid core and the outer mold to form a pneumatic tire.
After vulcanization, the core segments are moved in a tire radial direction to be taken out from the pneumatic tire.
Unfortunately, it may be difficult to take out the core segments from the pneumatic tire because the outer surface of each core segment has adhered strongly to the inner surface of the pneumatic tire. Accordingly, a forcible movement of the core segments may cause damages or an undesirable deformation on the pneumatic tire. Furthermore, in order to prevent such an undesirable deformation of the tire, another way where the core segments are taken out slowly from the tire may be considered. Unfortunately, the way described above may offer a long manufacturing cycle time and low productivity of the tires.
In order to solve the problem described above, modification of the outer surface shape of the rigid core, an increase of the divided number of core segments, and coating the outer surface of the rigid core with something may be considered.
Unfortunately, the modification of the outer surface shape of the rigid core may change the inner surface shape of the tire so that a tire performance lowers. Furthermore, the increase of the divided number of core segments may require a lot of cost for modifying the current equipments. Furthermore, coating the surface of the rigid core may cause a low adhesiveness between the rigid core and an unvulcanized rubber component. Therefore, it may be difficult to arrange the unvulcanized rubber component onto the rigid core accurately.